Heat exchanger for quenching thermally cracked gas

ABSTRACT

Quenching of thermally cracked gas of hydrocarbons is carried out by the use of a first stage heat exchanger and one of two or more second stage heat exchangers which are arranged in parallel and connected to the first stage one and each of which is used alternately after removal of deposited coke, whereby the operation of a thermal cracking furnace can be carried out continuously for much longer period than ever before.

United States Patent 1 1 lnvenwo lchiwTokumitsu 50 FieldofSearch 165/1,5, Tokyo; 97 Minoru Sugiyama, Tokyo; Souji Asano, Yamaguchiken, all of, Japan [56] References Cited [21] A ppLNo. 852,731 UNITEDSTATES PATENTS 523 d 555 5 2,877,866 3/1959 Mathisetal. 165/95 c [73] Assign ldemitsupdmchemicalcmltd. 2,886,483 5/1959 Rosenblad 165/95 Tokyo, Japan Primary Examiner-Charles Sukalo (32] Priority Se t. 12,1963 Attorney-FredCPhilpitt [33] Japan [31] 43/65238 [54] HEAT EXCHANGER FOR QUENCHING THERMALLY CRACKED GAS 10 Claims, 1 Drawing Fig. v [52] U.S.Cl 165/1, 165/95, 165/97 [51] lnt.Cl F28f 27/02 ABSTRACT: Quenching of thermally cracked gas of hydrocarbons is carried out by the use of a first stage heat exchanger and one of two or more second stage heat exchangers which are arranged in parallel and connected to the first stage one and each of which is used alternately after removal of deposited coke, whereby the operation of a thermal cracking furnace can be carried out continuously for much longer period than ever before.

PATENTEDJUL20IB7I HT EXCHANGER HT This invention relates to a method of, and an apparatus for quenching thermally cracked gas of hydrocarbons. More particularly it relates to a method of, and an apparatus for quenching thermally cracked gas of hydrocarbons in which heat exchangers are used in two stages; one heat exchanger is used in the first stage (upstream side) and two or more heat exchangers (downstream side) arranged in parallel and connected to the first stage heat exchanger, are used in the second stage, each of the heat exchangers in the second stage being alternately used after being freed of deposited coke. In another embodiment of the present invention, the oil hereinafter to be explained is injected at a part between the first stage heat exchanger and the second stage heat exchangers.

It has been a common practice to quench the thermally cracked gas in thermal cracking of hydrocarbons such as naptha or the like in order to prevent the secondary reaction of thermally cracked gas. ln such a case, the higher the thermal cracking temperature is, or the heavier the cracking feed stock is, the more the coke or the like is liable to deposit from the thermally cracked gas. This tendency is particularly pronounced in the downstream part of quenching heat exchangers. As the deposit of coke becomes pronounced, it narrows the inside of the tubes of the heat exchanger and reduces its efficiency. in order to remove the deposited coke, the operation of a cracking furnace is stopped and a mechanical means is employed for its removal. However, this happens so frequently that the reduction of the operation rate of the thermal cracking furnace is inevitable and this has been a great drawback to the operation of the thermal cracking furnace.

Accordingly, it is an object of the present invention to provide a method for prolonging the continuous operation period of a thermal cracking furnace. It is another object of the present invention to provide an apparatus for quenching thermally cracked hydrocarbon gas which enables to increase the operational efficiency of thermal cracking furnace.

These objects can be attained by the method and the apparatus of the present invention.

According to the present invention, the conventional quenching heat exchanger is replaced by quenching heat exchangers which consistof one heat exchanger in the first stage and two or more heat exchangers arranged in parallel in the second stage where deposit of coke is most pronounced and each one of the second stage heat exchanger is alternately used after removal of the deposited coke. When the heat exchanger in which the deposit of coke becomes too thick, it is subjected to mechanical cleaning and is stood ready for the next use. As the result of the present invention, the continuous operation period of the thermal cracking furnace can be extremely prolonged and the operation rate of the thermal cracking furnace can be elevated very much.

Further, according to another embodiment of the present invention, it is possible to promote the quenching effect of the said quenching heat exchanger by preventing the coke deposit on the inside wall of the tubes of heat exchanger. For this purpose, oil hereinafter to be explained is injected to the thermally cracked gas at a part between the first and the second stage heat exchangers.

As for the oil for quenching the thermally cracked gas, heavy bottoms (residual oil) of the thermal cracking of naphtha is preferable.

Preferable embodiments of this invention have been chosen for the purpose of illustration and description and are shown in the accompanying drawing, which is a schematic view of quenching heat exchangers of two stages with their relating instruments. 1 i

The heat exchangers consist of a first stage heat exchanger (upstream side) A and two or more of second stage heat exchangers (downstream side) B in the drawing. l and 3 are inlets for feed stock to be thermally cracked and for steam, respectively. 2 is a thermal cracking furnace. 4 is a horizontal pipe still. 6 is a steam generator. 5 is a water inlet and 7 is a steam outlet. 8 is an inlet of the oil which is injected between the first and the second stage heat exchangers.

The following examples will further illustrate this invention by referring to the drawing.

EXAMPLE 1 To a SELAS type thermal cracking furnace which cracks tons/day of light naphtha (b.p. 40 C--l70 C) as a feed stock hydrocarbon to produce ethylene etc., 0.6 part (by weight) of steam was supplied for every 1.0 part (by weight) of naphtha.

The thermally cracked gas from the heating pipe 4 ofa thermal cracking furnace 2 was introduced into a quenching heat exchanger A and quenched down to a temperature into a quenching heat exchanger A and quenched down to a temperature of 450550 C. After passing through one of the quenching heat exchangers B, it was further quenched down to a temperature of 350450 C. As a quenching medium, high pressure water is introduced at 5 into a steam generator 6 which is connected to the shell side of the heat exchangers A and B. Steam generated in the steam generator 6 leaves an outlet 7. Each of the second stage heat exchangers B was alternately used after removal of the deposited coke in the tubes of the heat exchangers and thus the period of the continuous operation could be prolonged considerably. Compared with about 60 days of continuous operation period attained in case where quenching was effected at the outlet temperature of 350450 C with only one conventional quenching heat exchanger, the continuous operating period of this example could be prolonged to about. I00 days.

EXAMPLE 2 In the same apparatus as that of example 1, heavy bottoms of thermal cracking of naphtha was supplied at a rate of 0.2 ton/hour to the position 8 in order to inject into the thermally cracked gas. As the result of injection of the oil, the period for continuous operation could be prolonged to about 120 days compared with 100 days in case of Example I. The injection of heavy bottoms of thermal cracking of naptha is carried out for the purpose of preventing the deposit of coke or the like and exceedingly prolongs the continuous operation period. The said heavy bottoms used is recovered by fractionation in the naphtha-cracking plant.

What we claim is:

1. A method for quenching thermally cracked hydrocarbon gases which comprises:

a. conducting the thermally cracked hydrocarbon gases from a thermal cracking furnace through a first heat exchanger zone in a first heat exchange stage in order to quench said thermally cracked hydrocarbon gases;

b. removing said gases from said first heat exchanger zone;

c. passing said gases through only one of at least two heat exchanger zones in a second heat exchange stage in order to further quench said gases;

cl. said at least two heat exchanger zones each having a sequential operation cycle consisting of l. a cleaning step,

2. a standby step, and 3. a heat exchange step;

c. said other(s) of said at least two heat exchanger zones being at either the cleaning step or the standby step of its operation cycle while said one of said at least two heat exchanger zones is at the heat exchange step of its operation cycle.

2. The method of claim .1 wherein said thermally cracked gases are derived from the thermal cracking of light naphtha having a boiling point between 40 C and C.

3, The method of claim 1 wherein said gases are quenched to a temperature of 450--550 C in said first heat exchange stage and are further quenched dovvn to a temperature of 350-450 C in said second heat exchange stage.

4. The method of claim 1 wherein said thermally cracked gases are quenched in said heat exchanger zones by indirect heat transfer with high pressure water.

5. A method for quenching thermally cracked hydrocarbon gases which comprises:

a. conducting thermally cracked hydrocarbon gases from a thermal cracking furnace through a first heat exchanger zone in a first heat exchange stage inorder to quench said thermally cracked gases;

b. removing said gases from said first heat exchanger zone;

c. injecting residual oil from the thermal cracking of naphtha into said gases in order to cool said gases;

d. passing said gases with the residual oil injected therein through only one of at least two heat exchanger zones in a second heat exchange stage in order to further quench said gases;

e. said at least two heat exchanger zones having a sequential operation cycle consisting of l. a cleaning step,

2. a standby step, and 3. a heat exchange step;

f. said other(s) of said at least two heat exchanger zones being at either the cleaning step or the standby step of its operation cycle while said one of said at least two heat exchanger zones is at the heat exchange step of its operation cycle.

6. The method of claim 5 wherein said gases are quenched to a temperature of 450550 C in said first heat echange stage and are further quenched down to a temperature of 350450 C in said second heat exchange stage.

7. An apparatus for quenching thermally cracked hydrocarbon gases which comprises:

a. a first stage heat exchanger means for quenching said gases;

b. said first stage heat exchanger means having an inlet for said thermally cracked gases and an outlet for said thermally cracked gases;

c. at least two second stage heat exchanger means for further quenching said gases and being connected in parallel to said first heat exchanger means;

d. said at least two second stage heat exchanger means each containing inlet means and outlet means for said thermally cracked gases;

c. said outlet for the first stage heat exchanger means connecting to said inlet means for each of said at least two second stage heat exchanger means;

f. said inlets for each of said at least two second stage heat exchanger means having value means; and

g. one of said valve means being open while the other said valve means is closed.

8. The apparatus of claim 7 wherein at least one heat exhanger means is a shell and tube heat exchanger.

9. The apparatus of claim 7 wherein both said first stage heat exchanger means and said at least two second stage heat exchanger means are shell and tube heat exchangers.

10. An apparatus for quenching thermally cracked hydrocarbon gases which comprise:

a. a first stage heat exchanger means for quenching said gases;

b. said first stage heat exchanger means having inlet means for said thermally first stage heat exchanger means having inlet means for said cracked gases and outlet means for said thermally cracked gases;

c. at least two second stage heat exchanger means for further quenching said gases that are connected in parallel to said first stage heat exchanger means;

d. said at least two second stage heat exchanger means each containing inlet means and outlet means for said thermally cracked gases; sald outlet means for the first stage heat exchanger means 

2. a standby step, and
 2. The method of claim 1 wherein said thermally cracked gases are derived from the thermal cracking of light naphtha having a boiling point between 40* C and 170* C.
 2. a standby step, and
 3. a heat exchange step; f. said other(s) of said at least two heat exchanger zones being at either the cleaning step or the standby step of its operation cycle while said one of said at least two heat exchanger zones is at the heat exchange step of its operation cycle.
 3. The method of claim 1 wherein said gases are quenched to a temperature of 450*-550* C in said first heat exchange stage and are further quenched down to a temperature of 350*-450* C in said second heat exchange stage.
 3. a heat exchange step; e. said other(s) of said at least two heat exchanger zones being at either the cleaning step or the standby step of its operation cycle while said one of said at least two heat exchanger zones is at the heat exchange step of its operation cycle.
 4. The method of claim 1 wherein said thermally cracked gases are quenched in said heat exchanger zones by indirect heat transfer with high pressure water.
 5. A method for quenching thermally cracked hydrocarbon gases which comprises: a. conducting thermally cracked hydrocarbon gases from a thermal cracking furnace through a first heat exchanger zone in a first heat exchange stage in order to quench said thermally cracked gases; b. removing said gases from said first heat exchanger zone; c. injecting residual oil from the thermal cracking of naphtha into said gases in order to cool said gases; d. passing said gases with the residual oil injected therein through only one of at least two heat exchanger zones in a second heat exchange stage in order to further quench said gases; e. said at least two heat exchanger zones having a sequential operation cycle consisting of
 6. The method of claim 5 wherein said gases are quenched to a temperature of 450*-550* C in said first heat echange stage and are further quenched down to a temperature of 350*-450* C in said second heat exchange stage.
 7. An apparatus for quenching thermally cracked hydrocarbon gases which comprises: a. a first stage heat exchanger means for quenching said gases; b. said first stage heat exchanger means having an inlet for said thermally cracked gases and an outlet for said thermally cracked gases; c. at least two second stage heat exchanger means for further quenching said gases and being connected in parallel to said first heat exchanger means; d. said at least two second stage heat exchanger means each containing inlet means and outlet means for said thermally cracked gases; e. said outlet for the first stage heat exchanger means connecting to said inlet means for each of said at least two second stage heat exchanger means; f. said inlets for each of said at least two second stage heat exchanger means having value means; and g. one of said valve means being open while the other said valve means is closed.
 8. The apparatus of claim 7 wherein at least one heat exhanger means is a shell and tube heat exchanger.
 9. The apparatus of claim 7 wherein both said first stage heat exchanger means and said at least two second stage heat exchanger means are shell and tube heat exchangers.
 10. An apparatus for quenching thermally cracked hydrocarbon gases which comprise: a. a first stage heat exchanger means for quenching said gases; b. said first stage heat exchanger means having inlet means for saiD thermally first stage heat exchanger means having inlet means for said cracked gases and outlet means for said thermally cracked gases; c. at least two second stage heat exchanger means for further quenching said gases that are connected in parallel to said first stage heat exchanger means; d. said at least two second stage heat exchanger means each containing inlet means and outlet means for said thermally cracked gases; e. said outlet means for the first stage heat exchanger means connecting to said inlet means for each of said at least two second stage heat exchanger means; f. inlet means for injecting oil to cool said thermally cracked gases which is located between said first-step heat exchanger means and said at least two second stage heat exchanger means; g. said inlets for each of said at least two second stage heat exchanger means having valve means; and h. one of said valve means being open while the other of said valve means is closed. 